Chingford Municipal Offices Geotechnical and geoenvironmental ground investigation report and remediation strategy

Transcription

1 CHINGFORD MUNICIPAL OFFICES Geotechnical and geoenvironmental ground investigation report and remediation strategy Copyright: Card Geotechnics Limited Card Geotechnics Limited ("CGL") has prepared this report in accordance with the instructions of Fairview New Homes ("the Client") under the terms of its appointment for consulting engineering Fairview New Homes Chingford Municipal Offices Geotechnical and geoenvironmental ground investigation report and remediation strategy Revision services by the Client. The report is for the sole and specific use of the Client, and CGL shall not be responsible for any use of the report or its contents for any purpose other than that for which it was prepared and provided. Should the Client require to pass copies of the report to other parties for information, the whole of the report should be so copied, but no professional liability or warranty shall be extended to other parties by CGL in this connection without the explicit written agreement thereto by CGL. Author Adam Cadman, Engineer MSc BSc (Hons) FGS Keisha Smith, Senior Engineer MSc BSc(Hons) AMIEnvSc Checked Richard Ball, Principal Engineer BSc MSc CEng MICE FGS April, 202 Ian Marychurch, Director MSc BSc CEng MICE CGeol FGS Approved Ian Marychurch, Director MSc BSc CEng MICE CGeol FGS Reference CG/5807A Revision 0 Issue Date April 202 April 202 Card Geotechnics Limited 4 Godalming Business Centre, Woolsack Way, Godalming, Surrey, GU7 XW Telephone:

2 CHINGFORD MUNICIPAL OFFICES Geotechnical and geoenvironmental ground investigation report and remediation strategy CHINGFORD MUNICIPAL OFFICES Geotechnical and geoenvironmental ground investigation report and remediation strategy Contents EXECUTIVE SUMMARY 5. INTRODUCTION 7 2. SITE CONTEXT 8 2. Site location Site description Proposed development 9 3. DESK STUDY 0 3. General Historical development Environmental disclosure report 3.4 Published geology Previous ground investigation Hydrogeology and hydrology Preliminary conceptual site model Preliminary conceptual site model Potential sources of contamination Potential pathways Potential receptors Preliminary risk assessment 6 4. PRESENT GROUND INVESTIGATION 9 4. Fieldwork Laboratory testing Chemical Geotechnical Groundwater and soil gas monitoring 2 5. GROUND AND GROUNDWATER CONDITIONS Summary Made Ground General fill Historic Topsoil London Clay Formation Desiccation Groundwater Soil gas GROUND CONTAMINATION Soil Risks to human health (longterm chronic risks) Groundwater Waste disposal CONCEPTUAL SITE MODEL AND RISK ASSESSMENT General Soil gases Soil contaminants GEOTECHNICAL RECOMMENDATIONS General Foundations Desiccation Floor slabs Excavations Pavement design Drainage Buried concrete REMEDIATION STRATEGY Background conditions Remediation requirements Capping layer Material management and waste classification Gas protection measures Buried services Health and safety Verification report 48 FIGURES Site location plan 2 Existing site layout plan and exploratory hole location plan 3 Cu versus level 4 Moisture content versus level CG/5807A Revision 2 CG/5807A Revision 3

3 CHINGFORD MUNICIPAL OFFICES Geotechnical and geoenvironmental ground investigation report and remediation strategy CHINGFORD MUNICIPAL OFFICES Geotechnical and geoenvironmental ground investigation report and remediation strategy 5 SPT N versus level 6 Conceptual site model APPENDICES A Photographs B Indicative proposed site layout C Historic mapping D Environmental disclosure report E Exploratory hole records F Chemical analysis G Geotechnical analysis H Monitoring records I Import specification EXECUTIVE SUMMARY Fairview New Homes (Fairview) has instructed Card Geotechnics Limited (CGL) to undertake a desk study and intrusive investigation to assess the ground conditions on site and to provide information as to potential contamination and geotechnical issues in relation to the proposed redevelopment of the site of the former Chingford Municipal Offices, off the Ridgeway in Chingford. The site is located at 6 The Ridgeway and is generally level. The surrounding ground slopes down towards the north and northwest, into the Lea River Valley. The presence of a 2m high retaining wall along the northern boundary of the site indicates that levels may have been made up to their current values in this area. The proposed development is residential and includes terraced houses and apartment blocks. Desk study information obtained for the site does not indicate any significantly contaminative uses in the site s history. An environmental statutory report has been obtained for the site and no significant items are recorded. The site is located on the London Clay Formation, a nonaquifer, and the site is not within a source protection zone. An intrusive investigation comprising three cable percussion boreholes to 20m below ground level (mbgl), five machine trial pits to 4mbgl, and 0 handdug pits, was undertaken in October 20. Soil samples were obtained for chemical and geotechnical laboratory testing and monitoring standpipes were installed in the boreholes. Insitu testing (SPT) was undertaken within the boreholes. The ground conditions encountered generally comprised a limited thickness (0.06m to 0.65m) of Made Ground, increasing to 2.2m in the northeast of the site supporting the suggestion that ground levels in this area have been raised over London Clay to 20mbgl. The Made Ground was typically variable, comprising loose to medium dense granular material, with historic clayey topsoil encountered generally. Groundwater was recorded as perched at the surface of the London Clay. Soil borne gas monitoring recorded no significant sustained flows, and a maximum CO 2 concentration of 0.%. CG/5807A Revision 4 Limited contamination was recorded within the Made Ground, comprising elevated lead concentrations in three shallow locations (max. depth 0.3m) and Polycyclic Aromatic Hydrocarbons (PAH), including benzo(a)pyrene, within the general fill Made Ground across the site. No significant contamination was recorded within the Historic Topsoil and underlying subsoils. Boron and Nickel concentrations within groundwater samples were CG/5807A Revision 5

4 CHINGFORD MUNICIPAL OFFICES Geotechnical and geoenvironmental ground investigation report and remediation strategy CHINGFORD MUNICIPAL OFFICES Geotechnical and geoenvironmental ground investigation report and remediation strategy found to exceed drinking water guidance values, however this is not considered significant as the water on site will not be used for drinking and is unlikely to come into contact with identified receptors. The Made Ground on site is generally suitable for disposal within a nonhazardous landfill facility with the exception of sample in trial pit TP0 which is Hazardous for disposal based on recorded hydrocarbon (diesel range) concentrations. However, the WAC testing analysis indicates that the material may be suitable for disposal within cells with a standard of containment consistent with nonhazardous wastes, subject to acceptance from the chosen landfill facility. The natural ground can be disposed at an inert landfill as listed inert waste. It is recommended that foundations are taken into the London Clay to a minimum depth of mbgl or 0.3m into the London Clay, whichever is deeper. They should generally be designed based on an allowable bearing pressure of 75kPa and the recommendations of NHBC building near trees should be accommodated in the design of the foundation depth. Desiccation testing was undertaken on London Clay samples, and no significant desiccation was recorded. Notwithstanding this, the London Clay is of high volume change potential and the NHBC guidelines should be adopted in the selection of foundation depths and foundation construction. Suspended floor slabs are recommended for the proposed development. Excavations in the London Clay are likely to be stable in vertical cut over the short term, but will require battering back if they are to remain stable over the longterm, typical batter angles are /3.5 for longterm stability. The Made Ground is unlikely to remain stable in excavation and will require side support/battering during construction. Pavements should be designed to a CBR of 2%. Soakaway drainage is not recommended due to the impermeability of the London Clay.. INTRODUCTION Fairview New Homes (Fairview) is considering the redevelopment of the former Chingford Municipal Officers, Chingford, London. The proposed development comprises the demolition of the existing structures, with the exception of the old Town Hall building, and the construction of terraced houses, 3 No. residential apartment blocks and associated private gardens, access ways and communal amenities. Card Geotechnics Limited (CGL) has been commissioned by Fairview to undertake a desk based study and geotechnical and geoenvironmental intrusive investigation. The objectives of the investigation are to: Provide information on the ground conditions; Identify the presence of any contamination in the soils onsite; Determine the prevalent ground gas regime; Provide a remediation strategy for appropriate remediation, waste management and gas protection measures, if required; Provide recommendations on foundations, substructure and infrastructure design, and ground movements relating to the removal of trees on site. This report details the work undertaken and presents information that may be used in the planning, design and construction of the development. Where Made Ground is to remain on site, a capping layer 600mm and 450mm thick is recommended for private gardens and managed communal space respectively, to Fairview New Homes typical details with a minimum of 50mm topsoil over subsoil and a geotextile separator. Where the Made Ground is to be removed from site, a 300mm topsoil layer is recommended over the Historic Topsoil/London Clay as a growth medium for gardens. The site is characterised broadly as Characteristic Situation 2 with regard to gas protection, and appropriate protection measures are recommended. Test results indicate that buried concrete in the London Clay should be designed for Design Sulphate class DS5, and ACEC class AC4s. A Design Chemical (DC) Class for castinsitu concrete of DC3 is deemed to be appropriate based on the available information. CG/5807A Revision 6 CG/5807A Revision 7

5 CHINGFORD MUNICIPAL OFFICES Geotechnical and geoenvironmental ground investigation report and remediation strategy CHINGFORD MUNICIPAL OFFICES Geotechnical and geoenvironmental ground investigation report and remediation strategy 2. SITE CONTEXT The existing site layout is presented in Figure 2 and photographs of the site are provided in Appendix A. 2. Site location The site is located at 6 The Ridgeway, Chingford, London, E4 6PP. The National Grid Reference for the approximate centre of the site is 53820, The site location is presented in Figure. 2.2 Site description The site is generally rectangular in shape fronting The Ridgeway between a Fire Station (to the west) and St Egberts Way (to the east) and is currently occupied by the former Chingford Municipal Offices, including the former Town Hall building in the eastern corner of the site, and associated access ways, hardstanding and car parking. A small pond is located within the quadrant of the existing Municipal Offices. The majority of the site is at an elevation of 56mOD reducing to approximately 55mOD in the southern area of the site. 2.3 Proposed development The proposed development comprises the demolition of the majority of the existing Municipal Office buildings on the site, with the exception of the Town Hall structure, and the construction of low level terraced residential units with private gardens and apartment blocks with associated managed amenity space. An indicative site layout is presented in Appendix B. A square car park is located in the north western area of the site. This area of the site is at a typical elevated of 57mOD, reducing by approximately one metre on the boundary with the main body of the site. The site is bound to the southeast by The Ridgeway, the northeast by St Egberts Way, the northwest by residential properties and the southwest by a Fire Station and College Gardens. A sheet pile retaining wall is present along much of the northwestern site boundary (excluding the area of the square car park) with a retained height of around 2m. This retaining structure extends partially along the northeastern site boundary, terminating at a crib lock retaining wall along St. Egberts Way. The majority of the northeastern site boundary (fronting St Egberts Way) is not retained, with a gently vegetated slope present between the road and the site fence. The site boundaries are generally lined with tress including lime, silver birch and blackthorn, particularly on the northern and southern site boundaries. Leyland Cypress trees are present on the boundary between the square car park area of the site and the Fire Station to the south. The site is located on the eastern edge of the River Lea Valley and the surrounding topography slopes to the northwest. CG/5807A Revision 8 CG/5807A Revision 9

6 CHINGFORD MUNICIPAL OFFICES Geotechnical and geoenvironmental ground investigation report and remediation strategy CHINGFORD MUNICIPAL OFFICES Geotechnical and geoenvironmental ground investigation report and remediation strategy 3. DESK STUDY The Corporation Yard is no longer noted on the map. According to Kelly s Directory the Town Hall was present as early as General A previous intrusive investigation and desk study review for the site was completed by Ground Engineering in June That report has been used to provide information on the site conditions and key points are summarised below. The original report should be reviewed for full details. The previous desk study review has been further supplemented by information obtained by CGL. 3.2 Historical development Ordnance Survey map extracts dating from 870 have been used to trace the historical development of the site. A brief summary of the development activities recorded on site and within the vicinity of the site is presented below with detailed information provided within the previous report. Copies of the historical maps are provided in Appendix C. The earliest available map dated 870 indicates the site and surrounding areas to be open fields with a Boys School located along the southeastern boundary. Residential development is seen in surrounding areas from the 896 map and at this time the site was a Nursery comprising a small collection of buildings along the southeastern site boundary and a rectangular structure (possible green house) in the northern area of the site. An excavation, labelled as The Chantry, is located to the north of the site on the 920 map. The site is relatively unchanged, although the possible greenhouse structure is no longer listed. Further development, primarily residential, occurs in the surrounding area and at the site between 920 and 965. A collection of buildings, including a Chingford Town Hall, are noted in the southern area of the site and Corporation Yard in the north with a car park in the northwest. The excavation to the north of the site was expanded, although the depth appears to be relatively shallow. Ground Engineering (2006). Site Investigation Report. Municipal Offices, 6 The Ridgeway, Chingford, London, E4. Report Reference No. C0509. June CG/5807A Revision 0 Minor layout changes have occurred between the construction of Chingford Town Hall and the present site layout, with the offices still present. No significant contaminative uses have been identified on site from the historical maps. However an electricity substation is shown offsite along the south western boundary. An excavation was located to the north of the site from 920 which has been eventually developed with residential properties. A review of the historical maps suggests that this excavation is likely to have been shallow, possibly for a playing field associated with the neighbouring college, and does not appear to have been backfilled. 3.3 Environmental disclosure report An environmental disclosure report was obtained to provide a summary of local conditions. Records include details of potentially contaminative activities onsite or at adjacent sites and the existence of nearby licenses and discharge consents that may have an impact on land quality at the subject site. The following summarises the most relevant findings and the full report is provided in Appendix D. There are no historical landfills or licensed waste management facilities within 250m of the site. The closest historical landfill was located 49m west of the site ceased in 964 and inert waste was deposited. There are no discharge consents within 250m of the site. The closest relates to discharge of sewage 90m north west of the site to a stream/river. There are no Local Authority Pollution Prevention and Controls within 250m of the site. The closest relates to a dry cleaners 457m east of the site. There are no Pollution Incidents to Controlled Waters within 250m of the site. The closest is 258m to the south west and was recorded as a minor incident. The receiving water body is unknown. There are no water abstractions within 250m of the site. The closest, 982m northwest of the site relates to the abstraction of surface water. The closest groundwater abstraction point (potable water abstraction) is 992m north west of the site. Both are operated by Thames Water Utilities Limited. CG/5807A Revision

7 CHINGFORD MUNICIPAL OFFICES Geotechnical and geoenvironmental ground investigation report and remediation strategy CHINGFORD MUNICIPAL OFFICES Geotechnical and geoenvironmental ground investigation report and remediation strategy The site is located in an area where less than % of the homes are above the action level for radon. Therefore no radon protection measures are required for new dwellings. There are 3 contemporary trade directory entries within 250m of the site. These relate to: oven cleaning (active), air conditioning and refrigeration contractors (inactive) and pest and vermin control (inactive). There are no fuel stations within 250m of the site. The site is located within a nitrate vulnerable zone. Areas of Adopted Green Belt, Special Areas of Conservation and Sites of Special Scientific Interest are located approximately 340m to the north of the site (Epping Forest). clayey sand and gravel with fragments of brick, ash, coal and glass. The Made Ground was encountered to depths of between 0.7m to.6m below ground level (bgl). The London Clay Formation was found to comprise firm orange brown mottled grey fissured clay becoming stiff generally from 3mbgl. From 7.5mbgl the London Clay Formation was described as stiff or very stiff fissured dark grey/dark brown clay. Selenite crystals and pyrite nodules were identified, with occasional shell fragments. Borehole BH04 encountered a layer of strong light grey concretionary limestone at 7mbgl, although this is considered likely to comprise a claystone. The London Clay Formation was proven to 20mbgl. Foundation inspection trial pits indicated the existing foundations to comprise concrete strip footings 0.45m thick and proven to a maximum depth of.35mbgl at one location. Geotechnical sulphate analysis indicated a maximum Design Sulphate Class of DS4 and an ACEC Class of AC Published geology The geology map 2 for the area indicates the site is underlain by the London Clay Formation. The London Clay Formation comprises a grey silty clay which becomes brown when weathered. The London Clay is typically 50m thick in the area of the site 2. At depth the London Clay Formation is underlain by the Lambeth Group, Thanet Sand Formation and Chalk. Chemical testing of soil samples indicated concentrations of metals and polycyclic aromatic hydrocarbons (PAH; i.e. benzo(a)pyrene) within the Made Ground, these contaminants were assessed against superseded guidance and will be further discussed in Section 5 of this report. One round of gas monitoring indicated flow rates of <0.l/hr and carbon dioxide and methane concentrations of <0.%v/v. 3.5 Previous ground investigation A ground investigation was conducted by Ground Engineering in March 2006, comprising 5 boreholes and 3 foundation inspection trial pits with associated insitu testing and chemical and geotechnical laboratory analysis. Gas monitoring wells were installed in two boreholes (BH2 and BH5) to 7mbgl with response zones within the Made Ground and London Clay Formation. The ground conditions encountered comprised Made Ground overlying the London Clay Formation. Hardstanding (tarmac/concrete) was encountered at the surface beneath which was granular subbase material and Made Ground. The Made Ground varied in composition from soft dark brown/orange brown sandy gravelly clay fill to dark brown 3.6 Hydrogeology and hydrology The Environment Agency website 3 indicates the site to be underlain by Unproductive Strata (London Clay Formation). These are rock layers or drift deposits with low permeability that have negligible significance for water supply or river base flow. According to the EA 3 the site is not situated within a groundwater source protection zone and is situated in an area not affected by flooding from rivers. The nearest surface water bodies are the William Girling Reservoir located approximately 800m to km to the east of the site with the River Lea beyond, and the River Roding located approximately 4km to the east of the site. A small ornamental pond has also been identified on site. 2 British Geological Survey. North London, England and Wales Sheet 256. Solid and Drift Edition CG/5807A Revision CG/5807A Revision 3

8 CHINGFORD MUNICIPAL OFFICES Geotechnical and geoenvironmental ground investigation report and remediation strategy CHINGFORD MUNICIPAL OFFICES Geotechnical and geoenvironmental ground investigation report and remediation strategy The site is located on the eastern edge of the Lea River Valley, with the River Lea supplying the William Girling Reservoir. The river generally flows in a southerly direction, towards central London. Perched groundwater was recorded in the previous investigation during a monitoring visit, resting above the London Clay within the Made Ground at around 0.8mbgl. No groundwater strikes were recorded during the drilling works. 3.7 Preliminary conceptual site model Historical contamination of land may present harm to human health and the environment. Current UK legislation stipulates that the risk associated with any potential land contamination is assessed and remediated, if necessary. Under the Town and Country Planning Act 947 (as amended), potential land contamination is a "material planning consideration" which means that a planning authority must consider contamination when they prepare development plans or consider individual applications for planning permission. It is the responsibility of the developer to carry out the remediation where it is required and satisfy the Local Authority that the remediation has been carried out as agreed. potentially have resulted in contamination of land. Information obtained from the previous investigation has also been used to identify potential sources of contamination. Based on the review of available information and findings from the previous intrusive ground investigation the following sources of risk have been identified: Made Ground The Made Ground across the site has been shown to contain locally elevated concentrations of metals and PAH against superseded guidance. Natural Ground The natural London Clay formation has been shown to contain elevated concentrations of sulphate. Groundwater The perched groundwater encountered beneath the site may potentially have been impacted by contamination in the Made Ground. Soil gas No elevated gas concentrations were encountered at the site. Further gas monitoring is required to confirm the risks posed to future site occupiers. Additionally, Part 2A of the Environmental Protection Act 990 requires that a significant sourcepathwayreceptor linkage exists to determine a site as contaminated land. This means that there has to be a contaminant present, a receptor that could be harmed by this contaminant, and a pathway linking the two. Part 2A deals with the contamination risk from a site in its current use, however the planning system requires that the proposed use is considered. Where remediation is carried out under the planning system, it should be ensured that the site is in such a condition that it would not still meet the definition of contaminated land under Part 2A Potential pathways Permeable soils The soils beneath the site comprise Made Ground over the London Clay Formation. The variable nature of the Made Ground, includes sand and gravel fill which could be relatively permeable and may potentially allow vertical and lateral migration of shallow contaminants. Groundwater Perched groundwater was encountered which could potentially facilitate lateral migration of contamination. 3.8 Preliminary conceptual site model A preliminary conceptual site model has been compiled for the subject site to determine the potential sources of contamination and the significance of potential pollutant linkages Potential sources of contamination Potential contamination sources can include current and historical activities on the site. A review of the site history has been undertaken to determine historic uses that could Inhalation and ingestion Contamination present in the shallow soils and groundwater could potentially result in ingestion or inhalation of contaminants, dust and vapour. Direct contact Direct contact with contaminated soils or groundwater could potentially result in uptake of contaminants through the skin. CG/5807A Revision 4 CG/5807A Revision 5

9 CHINGFORD MUNICIPAL OFFICES Geotechnical and geoenvironmental ground investigation report and remediation strategy Potential receptors CHINGFORD MUNICIPAL OFFICES Geotechnical and geoenvironmental ground investigation report and remediation strategy Table. Risk rating terminology. Current and future site occupiers The proposed future development includes residential properties. Construction workers This receptor could be affected by contamination during the development works as they are likely to be in close contact with potentially contaminated soils and groundwater, if present. Shallow groundwater Perched groundwater encountered within the Made Ground/London Clay Formation. Surface waters The nearest major surface water body is the William Girling Reservoir located approximately 800m to km to the east of the site. Buildings and structures Buried concrete and services can be at risk from chemically aggressive ground particularly within the London Clay Formation. Soil gases may also accumulate in buildings and structures presenting explosive risk, although existing limited data suggest no significant soil gas production. Plants and vegetation Phytotoxic contaminants (copper and zinc) within the underlying soils can present a risk to plants and vegetation at the site. Risk Rating High Risk Medium Risk Low Risk Negligible Risk Description Contaminants very likely to represent an unacceptable risk to identified targets Site probably not suitable for proposed use without mitigation Enforcement action possible Urgent action required Contaminants likely to represent an unacceptable risk to identified targets Site probably not suitable for proposed use without mitigation Action required in the medium term Contaminants may be present but unlikely to create unacceptable risk to identified targets Site probably suitable for proposed use without mitigation Action unlikely to be needed whilst site remains in current use If contamination sources are present they are considered to be minor in nature and extent Site suitable for proposed use without mitigation No further action required Using the above terminology, an assessment of the risks posed by the potential pollutant linkages at the site is outlined below in Table 2 (prior to mitigation measures or remediation) based on the conceptual model presented in Section 2.. Table 2. Preliminary risk assessment. 3.9 Preliminary risk assessment Source/medium Receptor Potential exposure route Risk Rating A preliminary risk assessment has been undertaken based on the findings of the information obtained from desk study review and the conceptual site model. The risks identified are in accordance with the DEFRA and Contaminated Land Report (CLR) 6 4, site prioritisation and categorisation rating system which is summarised in Table below. 4 M.J. Carter Associates (995). Prioritisation and Categorisation Procedure for Sites which may be Contaminated, Department of the Environment. CG/5807A Revision 6 Soil gases from onsite. Buildings & structures Migration of gases through the surface and via permeable soils Contaminants (i.e. metals, sulphates, PAH) within soils. CG/5807A Revision 7 Low Future site occupies Inhalation of gases & vapours Low Construction workers Current site users Construction workers Future site occupiers Current site users Buildings & structures Perched water Plants & Vegetation Direct ingestion of soil & dust, inhalation of particulates & vapours, indirect ingestion by means of dermal contact Direct contact with concrete and water supply pipes. Vertical migration of contaminants. Direct contact with phytotoxic contaminants Low Low Low to medium Low to medium Low Low to medium Low to medium Low to medium

10 CHINGFORD MUNICIPAL OFFICES Geotechnical and geoenvironmental ground investigation report and remediation strategy CHINGFORD MUNICIPAL OFFICES Geotechnical and geoenvironmental ground investigation report and remediation strategy The preliminary conceptual site model is based on the existing site setting and proposed residential development. The risks to receptors are generally considered to be low. The risk to human health of existing site users is considered to be low given the site is covered in hardstanding which provides a barrier and the site is currently vacant. However risks to constructions workers are considered to be low to medium as they may come in direct contact with potentially contaminated soils. Risks to future site occupiers are also considered to be low to medium due to potential contact in proposed garden areas. These risks have been further investigated and will be mitigated through appropriate use of PPE and remedial measures where necessary. The pyritic nature of London Clay provides a low to medium risk to underground concrete given the sulphate concentrations recorded during the previous investigation (maximum Design Sulphate Class of DS4 and a ACEC Class of AC4). Any contamination encountered within the Made Ground may potentially impact underground services such as water supply pipes. The risk to plants and vegetation is considered to be low to medium given the presence of phytotoxic metals within the Made Ground. This preliminary assessment and the information from the desk study review were used to inform the design of the intrusive investigation which is further discussed in the following sections. 4. PRESENT GROUND INVESTIGATION 4. Fieldwork The current intrusive investigation was undertaken between 24 th and 26 th October 20. The investigation comprised the formation of five machine excavated trial pits (TP0 to TP05) to a maximum depth of 4mbgl, three cable percussion boreholes (BH0 to BH03) to 20mbgl and ten hand dug trial pits (HDP0 to HDP0). The exploratory hole locations are indicated in Figure 2 and copies of the exploratory hole records are provided in Appendix E. The cable percussion boreholes were formed to a depth of 20mbgl and were positioned to characterise the ground conditions on the site. Standard Penetration Testing (SPT) was undertaken within each borehole and undisturbed samples were recovered for subsequent geotechnical laboratory testing. Gas monitoring wells were installed in each of the boreholes to facilitate ground gas and groundwater monitoring. The machine dug trial pits were positioned to identify and delineate desiccation with the shallow soils in the vicinity of trees and vegetation. For this purpose, geotechnical samples were recovered for moisture content and classification testing. TP03 was positioned furthest away from vegetation to provide a control for this testing 5. The hand dug trial pits were located to confirm the foundations of the existing structures and to identify the nature and extent of the retaining structure located in the northeastern area of the site. In order to obtain samples for laboratory chemical testing, and to fully characterise the near surface ground conditions across the site, the trial pit and borehole arisings were recorded, logged and representatively sampled by a suitably qualified engineer from CGL. The site was surveyed by a specialist service location contractor prior to the intrusive investigation and each exploratory hole location was scanned with a Cable Avoidance Tool (C.A.T), prior to the works commencing. The investigation was undertaken generally in accordance with the requirements of current UK guidance including BS and BS CG/5807A Revision 8 5 Building Research Establishment. (996). Desiccation in clay soils. BRE Digest British Standards Institution. (999). Code of practice for site investigations. BS5930:999 Inc. Amendment 2. CG/5807A Revision 9

11 CHINGFORD MUNICIPAL OFFICES Geotechnical and geoenvironmental ground investigation report and remediation strategy CHINGFORD MUNICIPAL OFFICES Geotechnical and geoenvironmental ground investigation report and remediation strategy 4.2 Laboratory testing ph Chemical Representative soil and groundwater samples were sent to I2 Analytical Limited (a UKAS and MCERTS accredited laboratory) for chemical testing. The analysis included the following contaminants and the results are included in Appendix F. 4.3 Groundwater and soil gas monitoring Groundwater level and soil gas monitoring visits have been undertaken on six separate occasions, between 3 rd November and 8 th December 20. Copies of the monitoring records are presented in Appendix H. Soil Organic Matter (SOM) Heavy metals including; arsenic, barium, beryllium, boron, cadmium, chromium, copper, lead, mercury, nickel, selenium, vanadium and zinc; Benzene, Toluene, Ethylbenzene, Xylenes (BTEX) compounds; Total Petroleum Hydrocarbons (TPH) and Polycyclic Aromatic Hydrocarbons (PAH); Total Monohydric Phenols; Total cyanide; Sulphate; and ph determination. In addition Waste Acceptance Criteria (WAC) testing was undertaken on four samples Geotechnical Representative soil samples were sent to Geolabs Limited and I2 Analytical Limited for geotechnical testing and the results are included in Appendix F and G. The following soil testing was undertaken. Particle size distribution (PSD); Atterberg Limits; Moisture Content; Quick undrained triaxial tests; Geotechnical sulphate to BRE SD; and CG/5807A 7 British Standards Revision Institution. (200). Investigation of potentially contaminated sites: Code of practice. BS075: CG/5807A Revision 2

12 CHINGFORD MUNICIPAL OFFICES Geotechnical and geoenvironmental ground investigation report and remediation strategy CHINGFORD MUNICIPAL OFFICES Geotechnical and geoenvironmental ground investigation report and remediation strategy 5. GROUND AND GROUNDWATER CONDITIONS 5. Summary The ground conditions encountered during the intrusive investigations are summarised below in Table 3. was generally between 0.05m and 0.4m thick, although deeper fill was encountered in BH02 to a depth of 2.2mbgl. The material generally comprised loose to medium dense, black brown, gravelly sand and sandy gravel with ash. The gravel is typically fine to coarse, with frequent cobbles of subangular flint, ceramic, clinker, brick and concrete. One SPT was undertaken within the Made Ground and indicated an SPT N value of 5, corresponding to a relative density of loose 6. Particle size distribution (PSD) testing indicates that this material is general silty/clayey gravelly sand to sand and gravel. Table 3. Summary of ground profile. The increased thickness of this material in the northeastern area of the site (BH02), and Stratum Depth to top of stratum (mbgl) Typical thickness (m) the 2m high sheet pile retaining wall, suggests that the site levels in this area were raised to their current level, possibly to provide carparking. TARMAC/CONCRETE to 0.39 [MADE GROUND GENERAL FILL] Comprising loose to medium dense black brown gravelly sand/sandy gravel with ash. Gravel fine to coarse with frequent cobbles subangular of flint, ceramic, clinker, brick and concrete. Brick rubble/fill encountered in BH03 and TP to 0.25 (absent in TP0) 0.05 to 0.4m 2.2 in BH02 (absent in TP0) 0.45 to.6 in previous investigation Historic Topsoil Historic Topsoil was encountered in each exploratory hole, except BH02 and BH03, at depths of between 0.08mbgl and 0.65mbgl below the general fill Made Ground deposits. This material was generally 0.4m to 0.65m thick overlying the London Clay Formation, and its presence further supports the suggestion that site levels in the northeastern corner (and in general) were raised to their current levels. Hydrocarbon odour present in BH02. [MADE GROUND HISTORIC TOPSOIL] Comprising soft to firm occasionally stiff green grey orange brown very silty clay with occasional black smearing. Occasional angular gravel of flint. Occasional black /organic inclusions and stained black rootlets. Organic odour present in TP0, TP03 and TP05. Soft to firm becoming stiff to very stiff with depth fissured orange brown & brownish grey sandy/silty CLAY with occasional claystone and selenite crystals to 0.65 (absent in BH02 & BH03) 0.25 to.6 2.2m in BH to 0.65 (absent in BH02 & BH03) Proven to 20mbgl The Historic Topsoil typically comprised soft to firm, occasionally stiff, green grey and orange brown, very silty clay, with occasional brown/black organic inclusions, and stained black decomposing rootlets. Occasional gravel sized angular flint was noted. An organic odour was present in TP0, TP03 and TP05 which may be attributed to the organic content of the soil. Insitu test results (hand shear vane HSV) indicate a mobilised shear strength (Cu) 8 in the order of 42kPa to 58kPa, or medium strength 6. A plot of Cu versus level is presented in Figure 3. [LONDON CLAY FORMATION] Classification parameters were determined by laboratory analysis and indicate the following parameter ranges; 5.2 Made Ground Moisture content between 36% and 38%; 5.2. General fill Liquid Limits between 62% and 79%; General fill was encountered at each exploratory hole location, except TP0, to depths of between 0.06mbgl and 0.25mbgl below the tarmac/concrete hardstanding. The material CG/5807A Revision 22 Plastic Limits between 27% and 33%; CG/5807A Revision 23

13 CHINGFORD MUNICIPAL OFFICES Geotechnical and geoenvironmental ground investigation report and remediation strategy CHINGFORD MUNICIPAL OFFICES Geotechnical and geoenvironmental ground investigation report and remediation strategy Plasticity Indices between 29% and 63%; and Modified Plasticity Indices between 45% and 53%. Modified Plasticity Indices between 28% and 5%. On this basis the historic topsoil may be classified as a clay of high to very high plasticity and has a medium to high volume change potential 9. A plot of moisture content versus level is presented in Figure London Clay Formation The London Clay Formation was encountered in each exploratory hole location at depths of between 0.25mbgl and 2.2mbgl and was proven to 20mbgl. The stratum generally comprised soft to firm, becoming stiff to very stiff with depth, fissured, orange brown and brownish grey sandy/silty CLAY with occasional claystones and selenite crystals. Insitu test results (standard penetration tests SPTs) indicated N values in the order of 7 to 33, corresponding to an undrained shear strength (Cu) of between 3.5kPa and 48.5kPa (based on f =4.5), based on established correlations 0. An N value greater than 50 was recorded in BH0 at 8mbgl, corresponding to a claystone band encountered between 8.3mbgl and 8.45mbgl. A plot of SPT N versus level is presented in Figure 5. Mobilised Cu 8 values as determined by the HSV were in the range of 38kPa to 90kPa quick undrained triaxial testing recorded Cu values in the range of 47kPa to 60kPa. These values are in general accordance with the values determined by SPT N /Cu correlation. A plot of Cu versus depth is presented in Figure 3 and indicates a general increase in shear strength with level. On this basis the following design Cu line is recommended for design: Cu = 406.5z (where z = metres below top of London Clay) On this basis the London Clay may be classified as a clay of very high plasticity with a high volume change potential 6. A plot of moisture content versus level is presented in Figure Desiccation Geotechnical analysis, including moisture content and Atterberg Limits, was undertaken on samples to specifically address the potential for heave associated with tree removal during the construction of the proposed development, and the implications of this on foundation design. The methodology adopted was that of BRE 42 (see Ref. 5) with trial pit TP03 forming the control trial pit. A plot of moisture content versus level is presented in Figure 4. The results do not indicate a significant change in moisture content with depth within the London Clay Formation, or a significant change in the Liquid Limit/Plastic Limit range. The moisture content/liquid Limit relationship indicates that the soil is not desiccated in these areas. It is also noted that the moisture content values recorded in the trial pits in close proximity to trees (TP0, TP02 and TP04) do not show a distinct variation to those recorded in the control trial pit (TP03), located further away from vegetation. On this basis the recorded Atterberg Limits and moisture contents may be considered as normal, equilibrium values. 5.5 Groundwater Groundwater was not encountered during the intrusive investigation. The results of the groundwater monitoring undertaken between 3 rd November and 8 th December 20 are summarised in Table 4 below. Laboratory analysis indicates classification parameter of; Moisture between 28% and 40%; Liquid Limits between 72% and 84%; Plastic Limits between 26% and 3%; Plasticity Indices between 45% and 53%; and 8 Terzaghi, K., Peck, R.B., Mesri, G. (996). Soil Mechanics in Engineering Practice, 3 rd Ed. 9 National HouseBuilding Council. (99). Building Near Trees Chapter Stroud, M.A. (975). The standard penetration test in insensitive clays and soft rocks. Proceedings of the European Symposium on Penetration Testing in the UK, 2, CG/5807A Revision 24 CG/5807A Revision 25

14 CHINGFORD MUNICIPAL OFFICES Geotechnical and geoenvironmental ground investigation report and remediation strategy CHINGFORD MUNICIPAL OFFICES Geotechnical and geoenvironmental ground investigation report and remediation strategy Table 4. Summary of groundwater levels. Groundwater level (mbgl) BH No. Response zone 03// 08// 7// 23// 02/2/ 08/2/ BH0 0.5 to 3.66 DRY BH to BH to 4.3 DRY 4.04 DRY* DRY* DRY DRY*. * Water noted at base of hole The results of the groundwater monitoring indicate a perched water table within the Made Ground, particularly in BH02 where the greatest thickness of Made Ground (general fill) was encountered (to 2.2mbgl). It is considered that the water levels in BH0 and BH02 may be a result of surface water recharge of the shallow soils resting above the London Clay Formation, and is not anticipated to represent a naturally high water table. It is possible that this water is essentially pooling within the Made Ground behind the sheet pile retailing wall in this area of the site. Further to this the local topography to the north of the site slopes relatively steeply towards the Lea Valley and a high water table would not be expected in such conditions. Table 5. Summary of soil gas results. Borehole Response zone Max CH 4 Max CO 2 Min O 2 Max VOC Max flow Sustained flow (mbgl) (% by vol) (% by vol) (% by vol) (ppm) (l/hr) (l/hr) BH 0.5 to [MG/LC] BH2 to [MG/LC] BH3 to [LC] MG Made Ground, London Clay London Clay Formation A maximum flow rate of 2.2l/hr has been recorded in borehole BH03, however no sustained flow has been recorded in any borehole to date. No significantly elevated methane concentrations have been recorded to date and a maximum carbon dioxide concentration of 0.% has been recorded. These results are discussed further in Section 9 of this report. 5.6 Soil gas Soil gas monitoring has been undertaken on 6 No. occasions between 3 rd November and 23 rd November 20 following the intrusive investigation and the results are summarised in Table 5 below. CG/5807A Revision 26 CG/5807A Revision 27

15 CHINGFORD MUNICIPAL OFFICES Geotechnical and geoenvironmental ground investigation report and remediation strategy CHINGFORD MUNICIPAL OFFICES Geotechnical and geoenvironmental ground investigation report and remediation strategy 6. GROUND CONTAMINATION 6. Soil Risks to human health (longterm chronic risks) The laboratory test results have been compared against the published Soil Guideline Values (SGVs) for the Residential (with homegrown produce) landuse category to assess the risk to human health from chemical contamination in the soils. Currently, SGVs have only been issued by the Environment Agency for a limited number of contaminants, namely selenium, mercury, arsenic, nickel, the BTEX compounds, phenol, polychlorinated biphenyls and cadmium. The SGVs have all been issued for a sandy loam soil with a Soil Organic Matter of 6% as standard. Chebychev Theorem has been applied. The Grubbs Test has also been used to identify potential outliers within datasets. Copies of the relevant statistical analysis are available on request. The assessment includes the chemical test results for the 2006 and 20 investigations for the Made Ground and natural soils. Where SGVs are not available, the soil results have been compared to Generic Assessment Criteria (GACs) that have been derived inhouse by CGL using the Contaminated Land Exposure Assessment (CLEA) model and version.06 of the CLEA software. The GACs represent conservative screening criteria and have been calculated using the default parameters for the standard land use scenario set out in the CLEA technical report and toxicological inputs in line with the requirements of Science Report SC05002/SR2 2 and, in the case of petroleum hydrocarbons, Science Report P5080/TR3 3. The GACs have been generated assuming a sandy loam soil type and a Soil Organic Matter of 6% for the Made Ground/Topsoil and % for natural ground, which are suitable assumptions for the site in question. More detailed information on the derivation of the CGL GACs can be provided upon request. The results of the assessment are set out below in Tables 6, 7 and 8 for the Made Ground, Historic Topsoil and London Clay respectively. Assessment against the SGVs and GACs is carried out at the 95 th percentile on the sample mean (designated US 95 ), which is considered to represent a reasonable worstcase scenario. Statistical assessment of the results has been completed in accordance with the recommendations set out in the recently published CL:AIRE guidance 4. In this regard, an assessment of the normality of the data has been undertaken. Where datasets are normally distributed the one sample t test has been applied to calculate the US 95. In the case of nonparametric datasets, the Environment Agency. (January 2009). Updated technical background to the CLEA model. Science Report SC05002/SR3. 2 Environment Agency. (January 2009). Human health toxicological assessment of contaminants in soil. Science Report SC05002/SR2. 3 Environment Agency. (February 2005). The UK Approach for Evaluating Human Health Risks from Petroleum Hydrocarbons in Soils. Science Report P5080/TR3. CG/5807A Revision 28 4 J. Lowe et al. (May 2008). Guidance on comparing soil contamination data with a critical concentration. CL:AIRE, CIEH & SAGTA. CG/5807A Revision 29

16 CHINGFORD MUNICIPAL OFFICES Geotechnical and geoenvironmental ground investigation report and remediation strategy CHINGFORD MUNICIPAL OFFICES Geotechnical and geoenvironmental ground investigation report and remediation strategy Table 6a Summary of soil contamination (risks to human health Made Ground). Contaminant SGV or 6% SOM for Residential (with homegrown produce) landuse Notes on soil saturation limits (SSL) Measured range US 95 Max conc/us 95 > Assessmen t Criteria? (Y/N) (mg/kg) (mg/kg) (mg/kg) # outlier detected SOM (%) * * * Arsenic N Cadmium 0 3 <0.24 N/A 6 N Chromium (total) N Chromium (III),00 40 N/A N Chromium (VI) 3.0 <.2 N/A N Lead Y Mercury (inorganic) 70 3 <0.3.4 N/A N Selenium <0.44 N/A N Boron * N/A * Copper 3, N/A N Nickel N/A N Zinc 8, N/A N Barium * N/A * Beryllium N/A N Vanadium N/A N Phenols <0.3<2 N/A N Cyanide * < N/A * BTEX compounds Benzene <0.00 N/A N Toluene 60 3 <0.00 N/A N Ethyl benzene <0.00 N/A N mxylene pxylene <0.002 oxylene <0.00 N/A N Notes:. = green; (a) = amber i.e. GAC set to model output, [SSL provided in square brackets] ; (b) = red i.e. SSL exceeded & considered to affect interpretation. GAC calculated in accordance with the CLEA Software Handbook ; (c) = based on direct contact; (d) GAC limited to SSL. 2. * = no value currently defined 3. Published Soil Guideline Value (Environment Agency, 2009) 4. Relates to Phenol (C6H5OH) only. 5. Concentrations for total xylenes should be compared to the value for mxylene for fresh spills and to oxylene for all other cases. 6. N/A US95 not calculated as maximum concentrations below assessment criteria data. Limit of detection exceeds assessment criteria N/A N Table 6b Summary of soil contamination (risks to human health Made Ground) cont. Contaminant SGV or 6% SOM for Residential (with homegrown produce) landuse Total Petroleum Hydrocarbons (TPH) Notes on soil saturation limits (SSL) Measured range US 95 Max conc/us95 > Assessmen t Criteria? (Y/N) (mg/kg) (mg/kg) (mg/kg) # outlier detected TPH aliphatic EC56 79 <0. N/A 2 N TPH aliphatic EC> <0. N/A N TPH aliphatic EC>80 59 <0. N/A N TPH aliphatic EC> (b) < N/A N TPH aliphatic EC>26 4,300 (b) <297 N/A N # TPH aliphatic EC>635 88,000 (b) N/A N TPH aromatic EC <0. N/A N TPH aromatic EC>78 60 <0. N/A N TPH aromatic EC>80 88 <0. N/A N TPH aromatic EC> < N/A N TPH aromatic EC> <22 N/A N TPH aromatic EC> [360] (a) <0460 N/A N TPH aromatic EC>235,200 [29] (a) N Polycyclic Aromatic Hydrocarbons (PAH) Acenaphthene 2,000 (b) < N/A N Anthracene 8,000 [46] (a) N/A N Benzo(a)anthracene 8 [0] (a) Y Benzo(a)pyrene Y Benzo(b)fluoranthene 24 [7.3] (a) Y Benzo(g,h,i)perylene 250 [0.] (a).347 N/A N Benzo(k)fluoranthene 24 [4.] (a) Y Chrysene 230 [2.6] (a).677 N/A N Dibenzo(a,h)anthracene 2.4 [0.02] (a) < Y Fluoranthene 2,200 [3] (a) N/A N Fluorene,800 [93] (a) <0. N/A N Indeno(,2,3cd)pyrene 24 [0.4] (a) Y Naphthalene N/A N Pyrene,600 [3] (a) N/A N Notes:. = green; (a) = amber i.e. GAC set to model output, [SSL provided in square brackets] ; (b) = red i.e. SSL exceeded & considered to affect interpretation. GAC calculated in accordance with the CLEA Software Handbook ; (c) = based on direct contact; (d) GAC limited to SSL. 2. N/A US95 not calculated as maximum concentrations below assessment criteria CG/5807A Revision 30 CG/5807A Revision 3

17 CHINGFORD MUNICIPAL OFFICES Geotechnical and geoenvironmental ground investigation report and remediation strategy CHINGFORD MUNICIPAL OFFICES Geotechnical and geoenvironmental ground investigation report and remediation strategy Table 7b Summary of soil contamination (risks to human health Historic Topsoil) cont. Table 7a Summary of soil contamination (risks to human health Historic Topsoil). Contaminant SGV or 2.5% SOM for Residential (with homegrown produce) landuse Notes on soil saturation limits (SSL) Measured range US 95 Max conc/ US 95 > Assessmen t Criteria? (Y/N) (mg/kg) (mg/kg) (mg/kg) # outlier detected SOM (%) * * * Arsenic n/a N Cadmium 0 3 < 0.2 n/a N Chromium (total) n/a Y Chromium (III), n/a N Chromium (VI) 3.0 <.2 n/a N Lead n/a N Mercury (inorganic) 70 3 < 0.3 n/a N Selenium <.0 n/a N Boron * n/a * Copper 3, n/a N Nickel n/a N Zinc 8, n/a N Barium * 8 0 n/a * Beryllium n/a N Vanadium n/a N Phenols < 2.0 n/a N Cyanide * <.0 n/a * BTEX compounds n/a Benzene 0.6 < 0.00 n/a N Toluene 270 < 0.00 n/a N Ethyl benzene 50 < 0.00 n/a N mxylene 6 00 oxylene 6 0 pxylene^ < 0.00 n/a N 98 < 0.00 n/a N Notes:. = green; (a) = amber i.e. GAC set to model output, [SSL provided in square brackets] ; (b) = red i.e. SSL exceeded & considered to affect interpretation. GAC calculated in accordance with the CLEA Software Handbook ; (c) = based on direct contact; (d) GAC limited to SSL. 2. * = no value currently defined 3. Based on published Soil Guideline Value (Environment Agency, 2009), adjusted for 2.5% SOM 4. GAC relates to Phenol (C6H5OH) only. 5. Based on the published SGVs for BTEX at 6% SOM (Environment Agency, 2009), adjusted for 2.5% SOM 6. Concentrations for total xylenes should be compared to the value for mxylene for fresh spills and to oxylene for all other cases. CG/5807A Revision 32 Contaminant SGV or 2.5% SOM for Residential (with homegrown produce) landuse Total Petroleum Hydrocarbons (TPH) Notes on soil saturation limits (SSL) Measured range US 95 Max conc/ US95 > Assessmen t Criteria? (Y/N) (mg/kg) (mg/kg) (mg/kg) # outlier detected TPH aliphatic EC56 4 < 0. n/a N TPH aliphatic EC>68 00 < 0. n/a N TPH aliphatic EC>80 25 < 0. n/a N TPH aliphatic EC> (b) <.0 n/a N TPH aliphatic EC>26 4,300 (b) < 2.0 n/a N TPH aliphatic EC>635 88,000 (b) < 8.0 n/a N TPH aromatic EC < 0. n/a N TPH aromatic EC> < 0. n/a N TPH aromatic EC>80 37 < 0. n/a N TPH aromatic EC>02 30 <.0 n/a N TPH aromatic EC> < 2.0 n/a N TPH aromatic EC> [50] (a) < 0 n/a N TPH aromatic EC>235,00 [2] (a) < 0 n/a N Hazard Index 2 n/a n/a n/a Polycyclic Aromatic Hydrocarbons (PAH) Acenaphthene,200 (b) < n/a N Anthracene 3,000 [9] (a) < n/a N Benzo(a)anthracene 3 [4.3] (a) n/a N Benzo(a)pyrene 2.4 [2.3] (a) n/a N Benzo(b)fluoranthene 23 [3.0] (a) n/a N Benzo(g,h,i)perylene 240 [0.05] (a) n/a N Benzo(k)fluoranthene 24 [.7] (a) < n/a N Chrysene 200 [.] (a) n/a N Dibenzo(a,h)anthracene 2.3 [0.0] (a) < 0.2 n/a N Fluoranthene,500 [47] (a) n/a N Fluorene,200 [38] (a) < 0.2 n/a N Indeno(,2,3cd)pyrene 23 [0.5] (a) < n/a N Naphthalene 3.7 < n/a N Pyrene,000 [5.5] (a) n/a N Notes:. = green; (a) = amber i.e. GAC set to model output, [SSL provided in square brackets] ; (b) = red i.e. SSL exceeded & considered to affect interpretation. GAC calculated in accordance with the CLEA Software Handbook ; (c) = based on direct contact; (d) GAC limited to SSL. 2. Hazard Index = (hazard quotients for each fraction); Hazard quotient = Fraction concentration AC CG/5807A Revision 33

18 CHINGFORD MUNICIPAL OFFICES Geotechnical and geoenvironmental ground investigation report and remediation strategy CHINGFORD MUNICIPAL OFFICES Geotechnical and geoenvironmental ground investigation report and remediation strategy Table 8a Summary of soil contamination (risks to human health London Clay) Contaminant SGV or % SOM for Residential (with homegrown produce) landuse Notes on soil saturation limits (SSL) Measured range US 95 Max conc/us95 > Assessment Criteria? (Y/N) (mg/kg) (mg/kg) (mg/kg) # outlier detected SOM (%) * * * Arsenic N/A N Cadmium 0 3 <0.20. N/A N Chromium (total) N/A Y Chromium (III), N/A N Chromium (VI) 3.0 <.2<5 N/A N Lead N/A N Mercury (inorganic) 70 3 < N/A N Selenium <0.3 N/A N Boron * N/A * Copper 3, N/A N Nickel N/A N Zinc 8, N/A N Barium * 5440 N/A * Beryllium N/A N Vanadium N/A N Phenols <0.3<2 N/A N Cyanide * <0.5< N/A * BTEX compounds Benzene <0.00 N/A N Toluene 20 5 <0.00 N/A N Ethyl benzene 65 5 <0.00 N/A N mxylene N/A N <0.002 pxylene N/A N oxylene <0.00 N/A N Notes:. = green; (a) = amber i.e. GAC set to model output, [SSL provided in square brackets] ; (b) = red i.e. SSL exceeded & considered to affect interpretation. GAC calculated in accordance with the CLEA Software Handbook ; (c) = based on direct contact; (d) GAC limited to SSL. 2. * = no value currently defined 3. Based on published Soil Guideline Value (Environment Agency, 2009), adjusted for % SOM 4. GAC relates to Phenol (C6H5OH) only. 5. Based on the published SGVs for BTEX at 6% SOM (Environment Agency, 2009), adjusted for % SOM 6. Concentrations for total xylenes should be compared to the value for mxylene for fresh spills and to oxylene for all other cases. 7. N/A US95 not calculated due to insufficient number of samples for suitable data set (3No. samples) data. Limit of detection exceeds assessment criteria Table 8b Summary of soil contamination (risks to human health London Clay) cont. Contaminant SGV or % SOM for Residential (with homegrown produce) landuse Total Petroleum Hydrocarbons (TPH) Notes on soil saturation limits (SSL) Measured range US 95 Max conc/us95 > Assessmen t Criteria? (Y/N) (mg/kg) (mg/kg) (mg/kg) # outlier detected TPH aliphatic EC56 24 <0. N/A 2 N TPH aliphatic EC>68 49 <0. N/A N TPH aliphatic EC>80 0 <0. N/A N TPH aliphatic EC> (b) < N/A N TPH aliphatic EC>26 4,200 (b) <2 N/A N TPH aliphatic EC>635 88,000 (b) <6 N/A N TPH aromatic EC <0. N/A N TPH aromatic EC>78 20 <0. N/A N TPH aromatic EC>80 5 <0. N/A N TPH aromatic EC>02 56 < N/A N TPH aromatic EC>26 30 <2 N/A N TPH aromatic EC> [60] (a) <0 N/A N TPH aromatic EC> [4.8] (a) <0 N/A N Polycyclic Aromatic Hydrocarbons (PAH) Acenaphthene 570 (b) <0.0. N/A N Anthracene 8,000 [7.7] (a) <0.0.4 N/A N Benzo(a)anthracene 7.5 [.7] (a) <0.2.2 N/A N Benzo(a)pyrene 2.2 [0.9] (a) <0. N/A N Benzo(b)fluoranthene 2 [.2] (a) <0..8 N/A N Benzo(g,h,i)perylene 240 [0.02] (a) < N/A N Benzo(k)fluoranthene 22 [0.7] (a) <0.2.7 N/A N Chrysene 60 [0.4] (a) <0.05. N/A N Dibenzo(a,h)anthracene 2.0 [0.004] (a) < N/A N Fluoranthene 820 [9] (a) < N/A N Fluorene 650 (b) < N/A N Indeno(,2,3cd)pyrene 20 [0.06] (a) <0.2.3 N/A N Naphthalene.5 < N/A N Pyrene 560 [2.2] (a) < N/A N Notes:. = green; (a) = amber i.e. GAC set to model output, [SSL provided in square brackets] ; (b) = red i.e. SSL exceeded & considered to affect interpretation. GAC calculated in accordance with the CLEA Software Handbook ; (c) = based on direct contact; (d) GAC limited to SSL. 2. N/A US95 not calculated due to insufficient number of samples for suitable data set (3No. samples) CG/5807A Revision 34 CG/5807A Revision 35

19 CHINGFORD MUNICIPAL OFFICES Geotechnical and geoenvironmental ground investigation report and remediation strategy Table 6 indicates elevated concentrations of metals, TPH and PAH are present within the Made Ground. The locations in which these contaminants were encountered (in concentrations exceeding guidance values) is summarised in Table 9 below: Table 9. Summary of contamination recorded in Made Ground. Contaminant Location Discussion Chromium HDP05 0.m Lead TP0 0.3m TP04 0.2m HDP05 0.m Polycyclic Aromatic Hydrocarbons (PAH) TP0 0.3m TP04 0.2m TP05 0.3m BH02.3m HDP04 0.7m HDP05 0.m TP 0.3m BH 0.4m BH2 0.3m BH3 0.3m BH3 0.7m Chromium concentrations were recorded in location within the Made Ground. It is noted however, that when speciated into Cr (III) and Cr (VI) oxidation states, both concentrations are below their respective guidance criteria (Note: Cr(VI) is considerably more toxic and concentrations of this oxidation state were recorded below the Limit of Detection of the laboratory equipment). Lead concentrations recorded were all within the top 0.3m of ground surface within the General Fill material acting as a subbase to the hardstanding on site. It is considered likely that this material will be removed from site as part of the initial site strip. Elevated PAHs were recorded within the General Fill. The most commonly encountered PAH was Benzo(a)pyrene, which potentially signifies an ash content within the general fill. Depending on final development levels, this material may potentially remain on site over the longterm and appropriate precautions/barriers may be required. Tables 7 and 8 indicate that the contaminants within the shallow Historic Topsoil and London Clay do not pose a risk to human health. Total chromium concentrations exceed the assessment criteria. However an assessment of the more toxic chromium (VI) indicates that concentrations found on site are below the limit of detection. The 2006 chemical data shows a higher limit of detection for the London Clay samples, which exceeds the assessment criteria for chromium (VI). However the more recent CGL results, which have a lower limit of detection, indicate that there is no risk to human health from chromium (VI). Some organic contaminants in Tables 6b, 7b and 8b exceed the GAC criteria denoted in the square brackets. These values are the soil saturation limits at which free product is theoretically expected to the present. Based on site observations, although a hydrocarbon odour was identified at BH2, free product has not been identified at the site and therefore the higher GAC criteria are considered applicable for this site. CG/5807A Revision 36 CHINGFORD MUNICIPAL OFFICES Geotechnical and geoenvironmental ground investigation report and remediation strategy 6.2 Groundwater Two groundwater samples were analysed for a range of contaminants. The results have been compared against EC Drinking Water Values (DWVs) and Freshwater Environmental Quality Standards (EQS) and are summarised in Table 0 below. Table 0. Summary of groundwater results Contaminant Freshwater EQS (g/l) EC Drinking Water Value (g/l) Measured range (g/l) No. of samples exceeding EQS No. of samples exceeding Drinking Water Value Arsenic Cadmium 5 5 < Chromium Lead Mercury < Selenium * 2 0 < * 0 Boron Copper Nickel Zinc (5000) Barium * (000) * 0 Beryllium (5) 4 * <0.2 0 * Vanadium 60 * < * Phenols 30 (0.5) 3 < 0 20 Cyanide <0 0 0 Sulphate (mg/l) TPH * (0) 3 <20 * 0 PAH * 0. 6 <0.04 * 0 Benzo(a)pyrene * 0.0 <0.0 * 0 Naphthalene 0 * <0.0 0 * Benzene 30 < Toluene 50 * < * Ethylbenzene * * <0.00 * * Xylenes 30 * < * Hardness (mg/l CaCO 3 ) * * * * ph Notes:. EQS varies with water hardness. Based on a hardness >250mg/l CaCO3. 2. * = No values defined or given 3. Concentration formerly prescribed within the Water Supply (Water Quality) Regulations Dutch Indication Level of Serious Contamination 5. EQS based on free cyanide which is more toxic than total cyanide. 6. Sum concentration of 4 PAH comprising benzo(b)fluoranthene, benzo(k)fluoranthene, benzo(ghi)perylene and indeno(,2,3cd)pyrene. 7. Limit of detection exceeds assessment criteria. CG/5807A Revision 37

20 CHINGFORD MUNICIPAL OFFICES Geotechnical and geoenvironmental ground investigation report and remediation strategy CHINGFORD MUNICIPAL OFFICES Geotechnical and geoenvironmental ground investigation report and remediation strategy Groundwater test results indicate that boron and nickel concentrations exceed stringent DWVs and phenols and sulphate exceed both EC DWVs and the Freshwater EQS. However, given that the groundwater on site is not a source of potable water, and is unlikely to come into contact with future receptors, the concentrations recorded are not considered to present a significant risk to sensitive receptors. 6.3 Waste disposal Total soils chemical results indicate that the natural ground and majority of the Made Ground would be classified as nothazardous. A single sample within Trial Pit TP0 at 0.3m depth classified as Hazardous due to elevated hydrocarbon concentrations within that particular sample. It is considered likely that this is due to a localised spillage, possibly from parked vehicles. The results indicate contaminant concentrations exceed the Inert Waste WAC criteria for each sample tested. On this basis the majority of the Made Ground material may be of at a suitably licensed nonhazardous landfill facility. The material in the area of TP0 has been classified as hazardous waste. However, as the WAC testing analysis indicates that the material has a low leaching potential and insitu testing has confirmed a CBR value of greater than 5% (value should not be used for design purposes), the material may be suitable for disposal within cells with a standard of containment consistent with nonhazardous wastes 5 subject to acceptance from the chosen landfill facility. The natural ground can be disposed at an inert landfill as listed inert waste 5. Waste Acceptability Criteria (WAC) testing has been undertaken on four samples of the Made Ground material 0.3m, 0.5m, 0.2m and and the results are summarised in Table below. Table. Summary WAC analysis. Sample location Contaminants concentrations exceeding Inert Waste WAC criteria Inert waste WAC criteria Stable nonreactive hazardous waste in nonhazardous landfill mg/kg mg/kg mg/kg Hazardous waste TP0 at 0.3mbgl TOC PAH 4.8% 640 3% 00 5% 6% TP02 at 0.5mbgl Sulphate ,000 50,000 TOC 3.5% 3% 5% 6% TP04 at 0.2mbgl PAH Antimony TOC 3.7% 3% 5% 6% PAH BH02 at.3mbgl Antimony Fluoride Sulphate ,000 50,000 CG/5807A Revision 38 5 Environment Agency (200). Waste acceptance at landfills. Guidance on waste acceptance procedures and criteria. Version. November 200. CG/5807A Revision 39